FRONT RELAY FOR AIR SUSPENSION

My rear suspension was sagging. My air compressor wouldn't come on, so, I figured it was blown. Replaced that with after-market compressor but still wouldn't run. Finally took it to Ford for diags. They said it was a bad wiring harness and the front relay switch was bad. I know there's a relay under the bumper, but they said it was higher than that one.
They want $600 parts and labor.
Any suggestions on whether or not I can get a new relay (and where the relay is)?
Is their price crazy?
(Note I already dropped $200 for the compressor)